Live line detector



Nov. 20, 1951 H. s. FETCH LIVE LINE DETECTOR Filed Feb. 27, 194ePatented Nov. 20, 1951 LIVE LINE DETECTOR Herbert Stanley Petch,Edgware, England, as-

signor to Elliott Brothers (London) Limited, London, England, a companyof Great Britain Application February 27, 1948, Serial No. 11,684 InGreat Britain August 1, 1945 Section 1, Public Law 690, August 8, 1946Patent expires August 1, 1965 15 Claims.

This invention relates to means for the purpose (hereinafter referred toas the purpose described) of indicating whether electric conductors areconnected to or disconnected from a source of supply. Such means are ofgreat value and prime importance from the point of view of theprotection of personnel engaged in tending or servicing electricalapparatus dealing with high voltages, such as transformers andswitchgear in electricity stations, since they may be utilised to give afinal check that all the prescribed precautionary measures have beentaken to isolate a piece of apparatus before work is done thereon.

It is the object of the invention to provide improved means of thischaracter which shall be reliable in operation, though simple incontruction, and which shall produce a readily recognisable visualindication when a conductor being tested is live.

According to the invention indicating means for the purpose describedcomprises a chamber containing two immiscible uids of differing speciiicinductive capacities, and a pair of electrodes so dispoed in relation tothe chamber that the production of an electric potential differencebetween the electrodes will cause a visible change in the distributionof the fluids within the chamber.

The indicating means according to the invention may be permanentlyattached to a conductor or mounted in a portable apparatus for manualuse.

In the accompanying drawing- Fig. 1 is an elevation, partly in section,of an indicating unit and illustrates by Way of example one form of theinvention for use as a permanent attachment to an electric conductor tobe tested or for incorporation in a portable apparatus,

Fig. 2 is a front view of the unit shown in Fig. 1 but to a smallerscale and with one electrode removed,

Fig. 3 illustrates by way of example one form of portable apparatusincorporating the unit shown in Fig. 1 but with parts removed for thesake of clarity, Y

Fig. 4 shows the means for capacity coupling one electrode to a metalcap in the apparatus of Fig. 3,

Fig. 5 is an illuminating device for use with the apparatus of Fig. 3,

Fig. 6 is a sleeve for holding the illuminating device of Fig. 5 inposition in the apparatus of Fig. 3,

Fig. 7 illustrates by way of example a modiiied form of unit connectedas a permanent attachment to a bus-bar,

Fig. 8- is a front view of the unit illustrated in Fig. 7 but to asmaller scale and indicating that the bus-bar is dead," and Fig. 9 is aview similar to Fig. 8 but indicating that the bus-bar is live.

Referring now to the form of the invention illustrated by way of examplein Fig. 1, the indieating unit comprises a circular disc electrode lhaving a shallow circular depression or recess 2 formed centrally of oneface and covered by a. thin glass sheet 3 constituting a window toprovide a closed cylindrical chamber which is of very small axialdimensions. This chamber is about half lled with air and the remainderof its volume is occupied by a liquid of high specific inductivecapacity, that is a non-conductor of electricity. Good results have beenobtained with a petroleum hydrocarbon (specic inductive capacity of 5)but other liquids may be employed. One suitable liquid is a commercialgrade of'gasoline. It is preferred to colour the liquid with a dyestuffor other substance ifit has no characteristic colour itself. It is to beunderstood that 'one of the fiuids in the chamber' of the unit abovereferred to may be the vapour of a liquid constituting the other iiuid,i. e. the chamber may be evacuated prior to the introduction oi theliquid.

The unit is completed by the provision of a second electrode 4 ofrestricted cross-sectional area at its operative end, which end ispresented axially to the centre of the chamber at a'very short distancefrom or in contact with the glass cover sheet 3. The unit is usuallyemployed with the plane of the glass sheet disposed vertically or butslightly inclined to the vertical.

In the use of the unit as an attachment to an electric conductor, thedisc electrode I is secured tc the latter` by means of the threadedshank 5..

by a spot of an insulating compound, with its v other end free orcarrying in some cases, an enlargement of spherical shape to increaseits capacity to earth. Conveniently, the disc electrode lis made frombrass, dull silver-plated,

and the glass cover sheet 3 is secured theretoby means of shellac. y y iWhen vthe conductor is connected to a source 'ratus employing the unitof Fig. 1.

of high potential, the capacity between the second electrode 4 and theearth is suiicient to cause the unit to give a characteristicindication, namely, the movement of liquid of high specific'inductivecapacity from its normal position of Arestvvithits''horizontalsurface substan; tally bisecting the chamber, as outlined by the line 6,into the central area of the chamber so that it assumes a tree-like formin outlin'e'iasrsA shown by the dot-chain line 'I. It is clear that ifchamber 2, 3 Were entirel'ylldiwith a -liquid'f'i such as gasoline, themovementzof'ithe liquid would be diiiicult to detectvisually. However;since chamber 2, 3 is filled Withtwofuid dielec.7 tries, one of which isliquid, movement. ofrthe'. liquid dielectric may be readilyl observed.

Reference will now be made to lliggsr..S-(iiflcli L illustrate by Way ofexample a portable appa- Thi's' -appai ratus comprises a tube'f ofinsulating material (Fig.` 3) into-which .is `fittedlazmetal- .capJ 9:electrically connectedtoV ametaltube- -I I) see Fig.;4)2. The latter isenclosed in a sleeve .II ofy insulating material .exceptfor theportionuIZ which enters the metal capfirandr-may be'adriving ttherein. Ametal cap i3 is itted-.intoftheend ofthe-insu?- lating=sleevefremoterfromff-the capita-@andi has'its external face I4 cutf-to'anangleaoff-45-degrees tothefiaxisfof theftube II',Jv the threaded-shank 5of-the'devicerI being-screwed into thecap I3 fso tha-tithe planefofTtheglassflsheet -3 is parallel to theeface Irisy BetWeenfthe-cap'I3fandthe` end ofthe-metal .tube Istheretis disposed `a=plug ofinsulating materialY I 5.-

As illustratedthere isfprovided afcapacity coupli-ngbetweenV the disc'electrode lI andthe metal capl 9 ffbyw binding' the insulating;sleevef- I I with copper Wire leandfelectricallyconnecting oneendnI'Ifof'theflattento the metal cap I3. Al'- though. `it isvpreferred3 =to1i employ 'capacity coupling, the dise-electrode I `maysbedirectly connected to themetal. 'capfBbyextendingthe metal tubeIllfandl securing`y the` metals-*capi I3A thereto.

The secondelectrode #dedie-posed inthe tube 8with one en'd. thereof.1presented .axially to the i centre for: the"l disci: electrode I and atai very short distance fronrrorrin contactwithithe glass cover sheet 3:AsV illustrated rthesecond' electrode V4- isl substantiallyhook"-shapedAand hasxits other"endsweated' to ar-'metalzring-IS which is sweated to ametal liner I9 in theginsulati'g tube 8:.

Whenl in use::thef indicator may "be vviewed through an inspectionaperturef20; theztvvo electrodes I and'dbeing mounted opposite 'thisapertue and kat a convenientfaviewig angle relative thereto;In'orderthat the'outline ofthe liquid maybe-more Aclearly seenttheportable apparatus is providedwith' an illuminatingtd'evice (see Fig. 59-comprisinga tubular metal casing ZI which is'-slid'.into the metal'.liner` IB'fsuchthat alamp 22"mourited' inv a lamp-1hol'der"23canfvill'uminate thefsurfa'ce'ofthefdiscfelectrode I.' A cylindricaltypei'batteryfzfispositioned inrthe'fcasing 21I andlitspositivetrelectrode 'is adapted. tolbef urged intovcontact:with-Ionef-contactof the lamp by means-of ay coil springI'25`i`vvi`1ic`hpresses''against theotherFend 'of thefbatteryM,th'eibattery casing :forming the: .negative =`electrode 1in thetusualmanner. The spring V251 is.' seatedi in a metal housing 2 uvhich isiaxiallymovable irr the casing Mia-ndprovded- W-itha fiance-.21;thatpart of they housing-26tting within the vcasing 2| `being encased ina sleeve 28 of insulating-material :so that there is no l electricalconnection between 4 the lamp holder or second contact of the lamp andthe negative electrode of the battery until the flange 2 abuts againstthe casing 2I thus completing the electrical circuit of the battery andlamp.A

Axial movement is impartedt the housing 25 by means of the spring 25 anda plug 2S of insulating material (see Fig. 6) which is secured in oneendzof a tubular metal member 39 slidably mounted on the tube 8. Theplug 29 has a threadedA portion' 3I of reduced diameter for screwingintol a threaded sleeve 32 secured in the tube 8;

In=.use', the tubular member 36 is rotated relatiirelyito'thetube 8 sothat the portion 3l of the p1ug,29 is screwed into the tube 8 until suchrotationxislzstopped by the flange 2'! abutting against the end of thecasing 2|, in which conditiontth'eu lamp 22 is energised. The apparatusis presented to a live conductor, metal cap 9 foremost-while grippingthe tubular metaly membenl,4 the=user being insulated from the con.-ductorby meansiof .the insulating tube ii. 4Horvever, there is,`suihcient capacity between the metal line I9 andthe hand ofthe usertoensure that` the second electrode.y t `is capacitycoupled toearth,through.the bodyoithe user,the liquidgivingthecharacteristicindication. l

Referringv now to Fig'.l 7, there` isi-illustrated'v `by Way ofrexamplea` modified-1indicatingY` unit attached to a bus-bar 33 -by means of aAmetal rod Strand-nut 35.l In this example; the unit com.- prisesa'-circular disc 36-of insulating material having a shallow circulardepression orv recess 31 =formed1 centrally of- 'one face and covered`by athinglass cover sheet 38 to form a closed cylindrical -ohambercontaining -a lliquidA and Iair as described with reference to Fig; 1.2The dise 35 is centrally mountedV on the rod S'which is also used as oneelectrode of the deviceand" is.in contact with the liquid;

In front of and spaced'from" the" glass sheet is-av second glass' cover"plate Y35i to provide-a shallow' cylindrical chamber. to lledi with. a

liquid. conductor of electricity; such ass water-.-

glass.. tovform av transparent conductor. The

latter-servesas rthe-secondI electrode lof the deviceandVin-orderito'increase its Ycapacity to earth, an annular member 4I isSecured between the two' :cover sheets 38 4and 4lflfwith its'internaledge contact with the transparent conductor. When nthe bus-barlis dead the'liquid of high specic inductive capacity is in its normalposi:- tion of rest. as shown'.bytlfie'line 42of'Fig.' 8.

.'However; when thetbus-barf-is live the liquid isrmoved so that itassumes theoutline indicated bythe line 43 of Figpg.

As illustrated inFigs. 8 andf'9; a reflector 44 isJ disposed centrallyinttherecess 3l 'such' that it reflects light when the bus-bar is deadbut is covered 'by'theliquid in the-recess 3l When'the This is iparticuiarlyf advantageous in those cases Where theindicating' deviceisfused in a darlcplacevandtthe operator Vmust use atorclr tozviewthef'liquid.

l. Indicating means for the purpose :described comprising. a;chamberzhavingr'at leastafshallow portion; two' visiblyrdistinguishable-r immiscible non-conducting uids of diieringspecicXinductive capacities;r Withinifsai'dchamber and aipair ofelectrodes disposed oppositesto. eachfctherat thefshallow (portion: aof. the f chamber with? the fluids: therebetween andffin' the; vicinityoitli'e surface between the two fluids.

2. Indicating means according to claim 1 wherein the chamber isconstituted by a disc having a shallow recess in one face covered by athin glass sheet, said disc also serving as one of said electrodes, andthe. other electrode is of ysmaller size than said disc `and ispresented toward the center of the chamber adjacent the glass coversheet.

3. Indicating means according to claim 1, which has an annularconducting member and in which the chamber is constituted by a dischaving a shallow recess in one face covered by a thin glass sheet, andin which one of said electrodes comprises a transparent conductor whichis in contact with said glass sheet, said annular conducting memberhaving an external diameter greater than that of the disc, surroundingsaid transparent conductor electrode and in contact therewith.

4. Indicating means according to claim 1, lwhich has an annularconducting member and in'which the chamber is constituted by a dischaving a shallow recess in one face covered by a thin glass sheet, saiddisc being of insulating material and having a central hole, in which lone Vof said electrodes comprises a rod extending into said hole incontact with said iiuids, and in which the other of said electrodescomprises a transparent conductor which is in contact with said glasssheet, said annular conducting mem- :ber havingl an external diametergreaterthan that of the disc, surrounding said transparent conductorelectrode and in contact therewith.

5. Indicating means according to claim 1 which has an annular conductingmember and in which the chamber is constituted by a disc having ashallow recess in one face covered by a thin glass sheet in which asecond thin glass sheet is mounted in parallel relation to the ilrstmentionedv thin glass sheet, but spaced therefrom, and in which one ofsaid electrodes comprises a transparent liquid conductor which iscontained between and in contact with the said glass sheets, saidannular conducting member having an external diameter greater than thatof the disc and surrounding said transparent conductor electrode betweensaid glass sheets and in contact therewith.

6. Indicating means according to claim 1 which has an annular conductingmember and in which the chamber is constituted by a disc having ashallow recess in one face covered by a thin glass sheet, said discbeing of insulating material and having a central hole, in which one ofsaid electrodes comprises a rod extending into said hole, and in contactwith said iluids, in which a second thin glass sheet is mounted inparallel relation to the first mentioned thin glass sheet, but spacedtherefrom and in which the other of said electrodes comprises atransparent liquid conductor which is contained between and in contactwith the said glass sheets, said annular conducting member having anyexternal diameter greater than that of the disc and surrounding saidtransparent conductor electrode between said glass sheets and in contacttherewith.

7. Indicating means for the purpose described comprisinga tube ofinsulating material, a metal cap at one end thereof, a metal tube withinthe tube of insulating material connected to said metal cap, a secondtube of insulating material surrounding the metal tube, an externalconducting sleeve around said second tube of insulating material, a pairof electrodes disposed opposite to each other within the first tube ofinsulating material, an electrical connection from the externalconducting sleeve to one of the electrodes, a chamber having at least ashallow portion, and two visibly distinguishable immisciblenon-conducting fluids of differing specic inductive capacities withinsaid chamber and between the electrodes, the surface between the twofluids being in the vicinity of the electrodes and at the shallowportion of the chamber.

8. Indicating means according to claim 7 wherein the second electrode iselectrically connected to a metal liner in the tube of insulatingmaterial and is adapted to be capacity coupled to earth through the handof the user.

9. A device for indicating whether an electric conductor is connected inan electric circuit, said device comprising a cylindrical chamber whoselength is small in comparison with its diameter, one end wall of saidchamber being a first electrode, the other end wail of said chamberbeing made of transparent insulating material, said chamber being closedand being partly filled with a visible liquid dielectric, a secondelectrode having an end portion which has a small crosssectional area,and means for maintaining said second electrode end portion proximate tosaid transparent end wall with said second electrode end portion inaxial alinement with the axis of said chamber.

10. A device for indicating whether an electric conductor is connectedin an electric circuit, said device comprising a cylindrical chamberwhose length is small in comparison With its diameter, said chamberbeing made of insulating material, a rst electrode of relatively smallcross-sectional area extending `into one end wall of said chamber, theother end wall of said chamber being transparent, said chamber beingclosed and being partly filled with a visible liquid dielectric whosedielectric constant is substantially diiTerent from that of air, and asecond electrode of transparent conducting material and having acircular face of substantially the same diameter as said chamber andmeans for maintaining said second electrode proximate to saidtransparent end wall with said electrode substantially transverse to theaxis of said iirst electrode rod.

11. A device for indicating whether an electric conductor is connectedin an electric circuit, said device comprising a housing which has alongitudinal axis, a rst electrode which is supported by said housingand which has a face of relatively large area which is transverse tosaid axis, and a second electrode of relatively small crosssectionalarea which is supported by said housing in a position proximate to andspaced from an interior portion of said first electrode face, saidhousing having a closed cavity positioned between said electrodes, saidcavity having end faces of relatively large area in comparison with thecrosssectional area of said second electrode, one of said end faceshaving a transparent window therein, said cavity being partly filledwith a visible liquid dielectric, the top level of said dielectric beingvisible through said window outside said housing when said housing isdisposed with its axis inclined from the vertical. Y

12. A device for indicating whether an electric conductor is connectedin an electric circuit, said device comprising a chamber having opposedtransverse end walls and a longitudinal side wall, at least one of saidend walls being transparent, the cross-sectional area of said chamberbeing large in comparison with its length, said chamber being partlylled with a liquid dielectric whose dielectric inexistant-differssubstantially *fronnthat vofair; vaxrst 4electrode.which Ahas Va'surface `which is-iproximate Yto ione of said end walls and. which ist:substantially transverse to the, axis: of said chamber. .and .Which hasa relatively large. crosse sectional area, and 'a second: electrodewhichis proximate-.to the other. of said end wails and which has arelativelysmall cross-sectionaLarea.

13. A device for-indicatingr Whetheran electric conductor isconnectedrin an electric circuit, said device comprising a housing whichhas a. longitudinal axis, a first electrode which is supported lay-said.housingandwhich. has a round face of relatively large areaiwhichis.transverse to said axis vvithJsaid axis extending through the centerofzsaifl` rstelectrcde faces and a second electrode'wliich has a`rod-portion of relatively small cross+sectionalarea-'and whichis'supported by said housingiwitli said'rod portion in alinement withthe axis-poi said. housing and with the free end ofsaid rod' portion.proximateto said .rst electrode, said. housing .beingY a. closed cavitypcsrtionedzbetween said electrodes. saidY cavity haw ingfroundend facesof approximately the same area as the ,area of .'saidiirstielectrodeface, the axis of saidz'cavity beingr alined with the axis of:said1housing, one of .said endtfaces having a transparent windowvtherein;said cavity being partly filled with a visible liquid dielectric Whosedielectricfconstant is substantially'diiferent from that of air, Ythe.toplevel of said dielectric being visible through said. window outsidesaid housing Whenisaidhousingr` is 'disposed' withpits axisinclinedromtheivertical;

14;,.A- device for lindicating whether an electric conductoris connectedin an electric circuit, said devicecomprising` a. cylindrical chamberWhose lenfgtl'risY small 'in' comparison with its diameter, said chamberbeing made of insulating material and'being closed andv being partlyfilled with a visible liquid dielectric; a rst electrode rod, saidchamber being mounted on said rod and: in axial alinement therewithand'wthsaid rod extending into an end Wall of said chamber, the otherend wall of said. chamber being transparentand a second felectrodefWhichfhas af circularface having substantially the same diameterras-f'said chambensaid second electrode being transparent, and meansforY maintaining saidsecondelectrode proximate to said transparent 'endWall and sub1L stantially transverseto the axisof saidchamber.

15. A-device for indicating Whether an electric conductor is connectedin an electricfcircuit; said device comprising .a housingwhich hasalongitudinal axis, a zfirst Yelectrode which is :supported by saidhousing and whichhas a face of vrelatively large area-Which istransverse to said axis, and-fa second eiectrode of. relativelysmalbcrossfsecti'onal area'which is supported by saidiiousingin`ai-position proximate to: and spacedafroman; interior portion of "said,first electrode' face, said :housing having a1 closed cavityApositionedbetweenfsaid electrodes, saidvcavity having end faceslcffrelatively large area in comparison with the 'cross-A sectional area'of'said second'electrode, the end face nearest'said secondelectrode having.a transa parent Window therein,b said rcavity beingf partly lledwth a.'visible dielectric, the`v topi' level f'of said dielectric being visibleAthrough said:windoxr outside.- said housing when said housingistdis+posed with its'faxis inclined :froml therverti'calf.

HERBERT STANLEY-FETCH..

REFERENCES. CITED.

The fol-lowing references are ofv recordin the nie offthis patent:

UNITED STATES PATENTS.

Number Name Date 2,442,614-- Norton i..-",June-l, 1948 FOREIGN PATENTS-Number Country Date:

558,351 Great BritainI Jan; 3, 1944 OTHER REFERENCES Publication titled-LiquidiDielectrics''by Gemant, published by `WileyA Sz' Sons inc.,1933;A pages .105; 106 andy 1G?.

